The film ends with a car exploding before the boy shouts "Allahu Akbar" with his arm raised next to the burnt wreckage.

The eight-minute video opens with apparent confessions about being spies by the three prisoners.

It comes a month after young Isa is thought to have first appeared in an IS propaganda film.

His grandfather Henry Dare said he believed the boy was the unidentified child involved in the footage which emerged in January and said he was merely being used as "a shield" by the terrorists.

Grace Dare was brought up as a Christian but converted to Islam and started using the first name Khadijah, her family said. She travelled to Syria in 2012 and married Swedish Islamic fighter Abu Bakr, who is believed to have been killed since.